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Saturday, March 16, 2013

A colorful tip

From the photo above, it might be difficult to guess what type of organism this is, but the next photo reveals a little more:

And the next even a little more:

This is a nemertean, or ribbon worm, that Eric discovered in a kelp holdfast on Salmon Creek Beach on 14 March 2013.  Specifically, it's Verrill's Ribbon Worm (Micrura verrilli).  [Addison Emery Verrill (1839-1926) was the first Professor of Zoology at Yale University.]  This individual was ~5 cm long and 2 mm wide.

Some ribbon worms are hard to identify, but this one is quite distinctive with its dramatic color pattern: purple-brown above marked with narrow white stripes, white below, and the standout orange and white coloration on the head.

I'll have to describe ribbon worms in greater detail in a future post, as they're one of my favorite groups of marine invertebrates.  For now, I'll just share a few more images from today.  

I hadn't seen this species before, so I spent some time watching this individual under the microscope.  Here's a close-up of the head region.  Can you see the long slit that runs from near the small orange spot back towards the tail (it looks like a fold or a furrow)?  It's called a cephalic slit and is thought to be involved with sensing chemical cues in the environment.  (Ribbon worms are active predators.)

Below is a view of the opposite end (the tail end).  The small, translucent projection is called a caudal cirrus.  Not all ribbon worms have one (the more common species of ribbon worms on Bodega Head don't).  This is a very curious structure, and after searching around a bit, I still couldn't find an explanation of how it might be used.

I'll leave you with one of my favorite images of the day.  I like it because this is such an attractive species, but also because it poses a question.  Why does this ribbon worm have such bright orange coloration at the tip of its head?

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